SPONTANEOUS GENERATION, SO CALLED. 259 



more and more of them were observed to lay eggs, which 

 were found to undergo development. 



Dating from Aristotle, who lived between three and four 

 hundred years B. c., it was nearly two thousand years before 

 any thing was known of the generation of insects ; the diffi- 

 culty here being that the young are first in a larval state and 

 bear no resemblance to the parents. Anterior to the experi- 

 ments of Eedi, it was thought that certain organic matters in 

 course of putrefaction developed living organisms, as mag- 

 gots in meat and the larvae in cheese. 



We refer to the experiments of Redi, made about the 

 year 1668, for the reason that these mark an era in our 

 knowledge of the process of generation. This observer, not- 

 ing that flies frequently lighted upon meat when it was ex- 

 posed, simply protected it by gauze, and found that no mag- 

 gots were developed, while other pieces of meat, placed un- 

 der the same conditions, except that the flies had free access 

 to them, developed maggots in great numbers. 1 By this sim- 

 ple experiment, Eedi showed that the maggots in putrefying 

 meat were produced by insects and not by the meat ; but 

 it remained for Swammerdam and Yallisneri a to study the 

 metamorphoses of insects, and to show how the eggs were 

 developed, first into sexless larvae, and finally into perfect 

 beings resembling the parents. It is curious to note the con- 

 dition of science anterior to Redi and Vallisneri, and com- 

 pare it with the ideas that are current at the present day. 

 When maggots appeared in putrefying meat, they were 

 thought to be produced by a spontaneous aggregation of 

 organic particles, simply because observers knew of no other 

 way in which these beings could come into existence. Now, 

 the advocates of spontaneous generation have the same ideas 

 as those advanced anterior to 1668 ; but, in the place of 

 meat, they have organic infusions, and for maggots, they sub- 

 stitute infusorial animalcules. It is possible that the discus- 



1 REDI, Ezperimenta circa Generationem Insectorum, Amstelaedami, 1686, p. 40. 



2 VALLISNERI, Istoria della Generazione, Venezia, 1721, p. 19. 



